Catalyst

ABSTRACT

Catalysts comprising nanostructured elements comprising microstructured whiskers having an outer surface at least partially covered by a catalyst material having the formula Pt x Ni y Au z , wherein x is in a range from 27.3 to 29.9, y is in a range from 63.0 to 70.0, and z is in a range from 0.1 to 9.6. Catalyst described herein are useful, for example, in fuel cell membrane electrode assemblies.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/413,173, filed Oct. 26, 2016, the disclosure of whichis incorporated by reference herein in its entirety.

BACKGROUND

Fuel cells produce electricity via electrochemical oxidation of a fueland reduction of an oxidant. Fuel cells are generally classified by thetype of electrolyte and the type of fuel and oxidant reactants. One typeof fuel cell is a polymer electrolyte membrane fuel cell (PEMFC), wherethe electrolyte is a polymeric ion conductor and the reactants arehydrogen fuel and oxygen as the oxidant. The oxygen is often providedfrom the ambient air.

PEMFCs typically require the use of electrocatalysts to improve thereaction rate of the hydrogen oxidation reaction (HOR) and oxygenreduction reactions (ORR), which improve the PEMFC performance. PEMFCelectrocatalysts often comprise platinum, a relatively expensiveprecious metal. It is typically desirable to minimize the platinumcontent in PEMFCs, increasing the catalyst activity per unit catalystsurface area (specific activity) and increasing the catalyst surfacearea per catalyst mass (specific surface area or specific area). The HORand ORR occur on the catalyst surface, so increasing the specificsurface area and/or the specific activity can reduce the devices' total(precious metal) catalyst loading to minimize cost. Sufficient platinumcontent, however, is needed to provide sufficient catalytic activity andPEMFC device performance. As such, there is a desire to increase thecatalyst activity per unit catalyst mass (mass activity). There are twogeneral approaches to increase the mass activity, namely the amount ofcatalyst needed to achieve a desired absolute performance, reducingcost.

To maximize specific area, PEMFC electrocatalysts are often in the formof nanometer-scale thin films or particles on support materials. Anexemplary support material for nanoparticle PEMFC electrocatalysts iscarbon black, and an exemplary support material for thin filmelectrocatalysts is whiskers.

To increase the specific activity, PEMFC Pt ORR electrocatalysts oftenalso comprise certain transition metals such as cobalt or nickel.Without being bound by theory, incorporation of certain transitionmetals into the Pt lattice is believed to induce contraction of the Ptatoms at the catalyst surface, which increases the kinetic reaction rateby modification of the molecular oxygen binding and dissociationenergies and the binding energies of reaction intermediates and/orspectator species.

PEMFC electrocatalysts may incorporate other precious metals. Forexample, HOR PEMFC Pt electrocatalysts can be alloyed with ruthenium toimprove tolerance to carbon monoxide, a known Pt catalyst poison. HORand ORR PEMFC electrocatalysts may also incorporate iridium tofacilitate improved activity for the oxygen evolution reaction (OER).Improved OER activity may improve the durability of the PEMFC underinadvertent operation in the absence of fuel and during PEMFC systemstartup and shutdown. Incorporation of iridium into the PEMFC ORRelectrocatalyst, however, may result in decreased mass activity andhigher catalyst cost. Iridium has relatively lower specific activity forORR than platinum, potentially resulting in decreased mass activity.Iridium is also a precious metal, and thereby its incorporation canincrease cost. PEMFC Pt electrocatalysts may also incorporate gold. Goldis known to be relatively inactive for HOR and ORR in acidicelectrolytes. Incorporation of gold can result in substantialdeactivation for HOR and ORR due to the propensity for gold topreferentially segregate to the electrocatalyst surface, blocking activecatalytic sites.

PEMFC electrocatalysts may have different structural and compositionalmorphologies. The structural and compositional morphologies are oftentailored through specific processing methods during the electrocatalystfabrication, such as variations in the electrocatalyst deposition methodand annealing methods. PEMFC electrocatalysts can be compositionallyhomogenous, compositionally layered, or may contain compositiongradients throughout the electrocatalyst. Tailoring of compositionprofiles within the electrocatalyst may improve the activity anddurability of electrocatalysts. PEMFC electrocatalyst particles ornanometer-scale films may have substantially smooth surfaces or haveatomic or nanometer-scale roughness. PEMFC electrocatalysts may bestructurally homogenous or may be nanoporous, being comprised ofnanometer-scale pores and solid catalyst ligaments.

As compared to structurally homogenous electrocatalysts, nanoporousPEMFC electrocatalysts may have higher specific area, thereby reducingcost. Nanoporous catalysts are comprised of numerous interconnectednanoscale catalyst ligaments, and the surface area of a nanoporousmaterial depends upon the diameter and volumetric number density of thenanoscale ligaments. Surface area is expected to increase as thenanoscale ligament diameter decreases and the volumetric number densityincreases.

One method of forming nanoporous PEMFC electrocatalysts is viadealloying of a transition metal rich Pt alloy precursor, such as a PtNialloy with 30 at. % Pt and 70 at. % Ni. During dealloying, the precursoris exposed to conditions where the transition metal is dissolved and thesurface Pt has sufficient mobility to allow exposure of subsurfacetransition metal and formation of nanoscale ligaments, which separatethe nanopores. Dealloying to form nanopores can be induced via freecorrosion approaches, such as exposure to acid or via exposure torepeated electrochemical oxidation and reduction cycles. Electrocatalystnanopore formation may occur spontaneously during electrochemicaloperation within a PEMFC or may occur via ex-situ processing prior toPEMFC operation.

In PEMFC devices, electrocatalysts may lose performance over time due toa variety of degradation mechanisms, which induce structural andcompositional changes. Such performance loss may shorten the practicallifetime of such systems. Electrocatalyst degradation may occur, forexample, due to loss of electrocatalyst activity per unit surface areaand loss of electrocatalyst surface area. Electrocatalyst specificactivity may be lost, for example, due to the dissolution ofelectrocatalyst alloying elements. Non-porous nanoparticle andnano-scale thin films may lose surface area, for example, due to Ptdissolution, particle sintering, and loss of surface roughness.Nanoporous electrocatalysts may additionally lose surface area, forexample, due to increased nanoscale ligament diameter and decreasednanoscale ligament density.

Additional electrocatalysts and systems containing such catalysts aredesired, including those that address one or more of the issuesdiscussed above.

SUMMARY

In one aspect, the present disclosure provides a catalyst comprisingnanostructured element comprising microstructured whiskers having anouter surface at least partially covered by a catalyst material havingthe formula Pt_(x)Ni_(y)Au_(z), wherein x is in a range from 27.3 to29.9, y is in a range from 63.0 to 70.0, and z is in a range from 0.1 to9.6 (in some embodiments, x is in a range from 29.4 to 29.9, y is in arange from 68.9 to 70.0, and z is in a range from 0.1 to 2.0; or even xis in a range from 29.7 to 29.9, y is in a range from 69.4 to 70.0, andz is in a range from 0.1 to 0.9). In some embodiments, the catalystmaterial functions as an oxygen reduction catalyst material.

In some embodiments, at least some layers comprising platinum and nickelhave been dealloyed to remove nickel from at least one layer. In someembodiments, there are pores with diameters in a range from 1 nm to 10nm (in some embodiments, in a range from 2 nm to 8 nm, or even 3 nm to 7nm) where the nickel was removed.

In some embodiments, catalysts described herein have been annealed.

Surprisingly, Applicants discovered the addition of gold to PtNicatalyst can substantially improve retention of mass activity, specificarea, and/or performance after accelerated electrocatalyst aging. Goldwas observed to improve the durability, whether incorporated into thebulk of the catalysts or at the surface of the catalyst, whetherincorporated into the catalyst before or after annealing, and whetherincorporated into or at the surface of the catalyst before or afternanoporosity was formed via dealloying.

Catalysts described herein are useful, for example, in fuel cellmembrane electrode assemblies.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of an exemplary catalyst described herein.

FIG. 2 is a schematic of an exemplary fuel cell.

FIG. 3A is a plot of the electrocatalyst mass activity of Examples 1-5and Comparative Example A catalysts, normalized to platinum content.

FIG. 3B is a plot of the electrocatalyst activity of Examples 1-5 andComparative Example A catalysts, normalized to total platinum groupmetal content.

FIG. 3C is a plot of the electrocatalyst surface area of Examples 1-5and Comparative Example A catalysts, normalized to platinum content.

FIG. 3D is a plot of the electrocatalyst surface area Examples 1-5 andComparative Example A catalysts, normalized to total platinum groupmetal content.

FIG. 3E is a plot of fuel cell performance of Examples 1-5 andComparative Example A catalysts.

DETAILED DESCRIPTION

Referring to FIG. 1, exemplary catalyst described herein 100 onsubstrate 108 has nanostructured elements 102 with microstructuredwhiskers 104 having outer surface 105 at least partially covered bycatalyst material 106 having the formula Pt_(x)Ni_(y)Au_(z), wherein xis in a range from 27.3 to 29.9, y is in a range from 63.0 to 70.0, andz is in a range from 0.1 to 9.6 (in some embodiments, x is in a rangefrom 29.4 to 29.9, y is in a range from 68.9 to 70.0, and z is in arange from 0.1 to 2.0; or even x is in a range from 29.7 to 29.9, y isin a range from 69.4 to 70.0, and z is in a range from 0.1 to 0.9).

Suitable whiskers can be provided by techniques known in the art,including those described in U.S. Pat. No. 4,812,352 (Debe), U.S. Pat.No. 5,039,561 (Debe), U.S. Pat. No. 5,338,430 (Parsonage et al.), U.S.Pat. No. 6,136,412 (Spiewak et al.), and U.S. Pat. No. 7,419,741(Vernstrom et al.), the disclosures of which are incorporated herein byreference. In general, nanostructured whiskers can be provided, forexample, by vacuum depositing (e.g., by sublimation) a layer of organicor inorganic material onto a substrate (e.g., a microstructured catalysttransfer polymer sheet), and then, in the case of perylene reddeposition, converting the perylene red pigment into nanostructuredwhiskers by thermal annealing. Typically, the vacuum deposition stepsare carried out at total pressures at or below about 10⁻³ Torr or 0.1Pascal. Exemplary microstructures are made by thermal sublimation andvacuum annealing of the organic pigment C.I. Pigment Red 149 (i.e.,N,N′-di(3,5-xylyl)perylene-3,4:9,10-bis(dicarboximide)). Methods formaking organic nanostructured layers are reported, for example, inMaterials Science and Engineering, A158 (1992), pp. 1-6; J. Vac. Sci.Technol. A, 5, (4), July/August 1987, pp. 1914-16; J. Vac. Sci. Technol.A, 6, (3), May/August 1988, pp. 1907-11; Thin Solid Films, 186, 1990,pp. 327-47; J. Mat. Sci., 25, 1990, pp. 5257-68; Rapidly QuenchedMetals, Proc. of the Fifth Int. Conf. on Rapidly Quenched Metals,Wurzburg, Germany (Sep. 3-7, 1984), S. Steeb et al., eds., ElsevierScience Publishers B.V., New York, (1985), pp. 1117-24; Photo. Sci. andEng., 24, (4), July/August 1980, pp. 211-16; and U.S. Pat. No. 4,340,276(Maffitt et al.) and U.S. Pat. No. 4,568,598 (Bilkadi et al.), thedisclosures of which are incorporated herein by reference. Properties ofcatalyst layers using carbon nanotube arrays are reported in the article“High Dispersion and Electrocatalytic Properties of Platinum onWell-Aligned Carbon Nanotube Arrays”, Carbon, 42, (2004), pp. 191-197.Properties of catalyst layers using grassy or bristled silicon arereported, for example, in U.S. Pat. App. Pub. No. 2004/0048466 A1 (Goreet al.).

Vacuum deposition may be carried out in any suitable apparatus (see,e.g., U.S. Pat. No. 5,338,430 (Parsonage et al.), U.S. Pat. No.5,879,827 (Debe et al.), U.S. Pat. No. 5,879,828 (Debe et al.), U.S.Pat. No. 6,040,077 (Debe et al.), and U.S. Pat. No. 6,319,293 (Debe etal.), and U.S. Pat. App. Pub. No. 2002/0004453 A1 (Haugen et al.), thedisclosures of which are incorporated herein by reference). Oneexemplary apparatus is depicted schematically in FIG. 4A of U.S. Pat.No. 5,338,430 (Parsonage et al.), and discussed in the accompanyingtext, wherein the substrate is mounted on a drum, which is then rotatedover a sublimation or evaporation source for depositing the organicprecursor (e.g., perylene red pigment) prior to annealing the organicprecursor in order to form the whiskers.

Typically, the nominal thickness of deposited perylene red pigment is ina range from about 50 nm to 500 nm. Typically, the whiskers have anaverage cross-sectional dimension in a range from 20 nm to 60 nm and anaverage length in a range from 0.3 micrometer to 3 micrometers.

In some embodiments, the whiskers are attached to a backing. Exemplarybackings comprise polyimide, nylon, metal foils, or other materials thatcan withstand the thermal annealing temperature up to 300° C. In someembodiments, the backing has an average thickness in a range from 25micrometers to 125 micrometers.

In some embodiments, the backing has a microstructure on at least one ofits surfaces. In some embodiments, the microstructure is comprised ofsubstantially uniformly shaped and sized features at least three (insome embodiments, at least four, five, ten, or more) times the averagesize of the whiskers. The shapes of the microstructures can, forexample, be V-shaped grooves and peaks (see, e.g., U.S. Pat. No.6,136,412 (Spiewak et al.), the disclosure of which is incorporatedherein by reference) or pyramids (see, e.g., U.S. Pat. No. 7,901,829(Debe et al.), the disclosure of which is incorporated herein byreference). In some embodiments, some fraction of the microstructurefeatures extend above the average or majority of the microstructuredpeaks in a periodic fashion, such as every 31^(st) V-groove peak being25% or 50% or even 100% taller than those on either side of it. In someembodiments, this fraction of features that extends above the majorityof the microstructured peaks can be up to 10% (in some embodiments up to3%, 2%, or even up to 1%). Use of the occasional taller microstructurefeatures may facilitate protecting the uniformly smaller microstructurepeaks when the coated substrate moves over the surfaces of rollers in aroll-to-roll coating operation. The occasional taller feature touchesthe surface of the roller rather than the peaks of the smallermicrostructures, so much less of the nanostructured material or whiskermaterial is likely to be scraped or otherwise disturbed as the substratemoves through the coating process. In some embodiments, themicrostructure features are substantially smaller than half thethickness of the membrane that the catalyst will be transferred to inmaking a membrane electrode assembly. This is so that during thecatalyst transfer process, the taller microstructure features do notpenetrate through the membrane where they may overlap the electrode onthe opposite side of the membrane. In some embodiments, the tallestmicrostructure features are less than ⅓^(rd) or ¼^(th) of the membranethickness. For the thinnest ion exchange membranes (e.g., about 10micrometers to 15 micrometers in thickness), it may be desirable to havea substrate with microstructured features no larger than about 3micrometers to 4.5 micrometers tall. The steepness of the sides of theV-shaped or other microstructured features or the included anglesbetween adjacent features may, in some embodiments, be desirable to beon the order of 90° for ease in catalyst transfer during alamination-transfer process and to have a gain in surface area of theelectrode that comes from the square root of two (1.414) surface area ofthe microstructured layer relative to the planar geometric surface ofthe substrate backing.

In some embodiments, the catalyst material comprises a layer comprisingplatinum and nickel and a layer comprising gold on the layer comprisingplatinum and nickel.

In some embodiments, layers comprising platinum and nickel have a planarequivalent thickness in a range from 0.4 nm to 70 nm (in someembodiments, in a range from 0.4 nm to 1 nm, 0.4 nm to 5 nm, 1 nm to 25nm, or even 1 nm to 10 nm) and layers comprising gold have a planarequivalent thickness (i.e., the thickness if deposited on asubstantially flat, planar substrate) in a range from 0.01 nm to 20 nm(in some embodiments, in a range from 0.01 nm to 10 nm, 0.01 nm to 5 nm,0.02 nm to 2.5 nm, or even 0.02 nm to 1 nm). In some embodiments, thelayer(s) comprising platinum and nickel collectively has a planarequivalent thickness up to 600 nm (in some embodiments, up to 575 nm,550 nm, 500 nm, 400 nm, 300 nm, 200 nm, 100 nm, 75 nm, 50 nm, 25 nm, 10nm, 5 nm, 2.5 nm, 1 nm, or even up to two monolayers (e.g., 0.4 nm); insome embodiments, in a range from 0.4 nm to 600 nm, 0.4 nm to 500 nm, 1nm to 500 nm, 5 nm to 500 nm, 10 nm to 500 nm, 10 nm to 400 nm, or even40 nm to 300 nm) and the layer comprising gold has a planar equivalentthickness up to 50 nm (in some embodiments, up to 45 nm, 40 nm, 35 nm,30 nm, 25 nm, 20 nm, 15 nm, 10 nm, 5 nm, 4 nm, 3 nm, 2 nm, 1 nm, amonolayer (e.g., 0.2 nm) or even less than a monolayer (e.g., 0.01 nm);in some embodiments, in a range from 0.01 nm to 50 nm, 1 nm to 50 nm, 5nm to 40 nm, or even 5 nm to 35 nm).

In some embodiments, the catalyst material comprises alternating layerscomprising platinum and nickel and layers comprising gold (i.e., a layercomprising platinum and nickel, a layer comprising gold, a layercomprising platinum and nickel, a layer comprising gold, etc.). In someembodiments, at least 2, 3, 4, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200,250, or even at least 275 sets of the alternating layers.

The thickness of an individual deposited catalyst layer may depend, forexample, on the areal catalyst loading of the layer and the catalystdensity. For example, the thickness of a single layer of Pt with 10micrograms of Pt per cm² planar area and density of 21.45 g/cm³deposited onto a planar substrate is calculated as 4.7 nm, and thethickness of a Ni layer with the same areal loading is 11.2 nm.

In some embodiments, the catalyst material comprises a layer comprisingplatinum, a layer comprising nickel on the layer comprising platinum,and a layer comprising gold on the layer comprising nickel. In someembodiments, the catalyst material comprises a layer comprising nickel,a layer comprising platinum on the layer comprising nickel, and a layercomprising gold on the layer comprising platinum. In some embodiments,the catalyst material comprises repeating sequential individual layersof platinum, nickel, and gold. In some embodiments, at least 2, 3, 4, 5,10, 15, 20, 25, 50, 75, 100, 150, 200, 250, or even at least 275 sets ofthe repeating layers.

In some embodiments, the catalyst material has an exposed gold surfacelayer.

In some embodiments, each layer independently has a planar equivalentthickness up to 100 nm (in some embodiments, up to 50 nm, 20 nm, 15 nm,10 nm, 5 nm, 4 nm, 3 nm, 2 nm, 1 nm, a monolayer (e.g., 0.2 nm), or evenup to less than a monolayer (e.g. 0.01 nm); in some embodiments, in arange from 0.01 nm to 100 nm, 0.01 nm to 50 nm, 0.1 nm to 15 nm, 0.1 nmto 10 nm, or even 1 nm to 5 nm).

In general, the catalyst can be deposited by techniques known in theart. Exemplary deposition techniques include those independentlyselected from the group consisting of sputtering (including reactivesputtering), atomic layer deposition, molecular organic chemical vapordeposition, molecular beam epitaxy, thermal physical vapor deposition,vacuum deposition by electrospray ionization, and pulse laserdeposition. Additional general details can be found, for example, inU.S. Pat. No. 5,879,827 (Debe et al.), U.S. Pat. No. 6,040,077 (Debe etal.), and. U.S. Pat. No. 7,419,741 (Vernstrom et al.), the disclosuresof which are incorporated herein by reference. The thermal physicalvapor deposition method uses suitable elevated temperature (e.g., viaresistive heating, electron beam gun, or laser) to melt or sublimate thetarget (source material) into a vapor state, which is in turn passedthrough a vacuum space, then condensing of the vaporized form ontosubstrate surfaces. Thermal physical vapor deposition equipment is knownin the art, including that available, for example, as a metal evaporatoror as an organic molecular evaporator from CreaPhys GmbH, Dresden,Germany, under the trade designations “METAL EVAPORATOR (ME-SERIES)” or“ORGANIC MOLECULAR EVAPORATOR (DE-SERIES)” respectively; another exampleof an organic materials evaporator is available from Mantis DepositionLTD, Oxfordshire, UK, under the trade designation “ORGANIC MATERIALSEVAPORATOR (ORMA-SERIES).” Catalyst material comprising multiplealternating layers can be sputtered, for example, from multiple targets(e.g., Pt is sputtered from a first target, Ni is sputtered from asecond target, and Au from a third, or from a target(s) comprising morethan one element (e.g., Pt and Ni)). If the catalyst coating is donewith a single target, it may be desirable that the coating layer beapplied in a single step onto the gas distribution layer, gas dispersionlayer, catalyst transfer layer, or membrane, so that the heat ofcondensation of the catalyst coating heats the underlying catalyst orsupport Pt, Ni, or Ir atoms as applicable and a substrate surfacesufficient to provide enough surface mobility that the atoms are wellmixed and form thermodynamically stable alloy domains. Alternatively,for example, the substrate can also be provided hot or heated tofacilitate this atomic mobility. In some embodiments, sputtering isconducted at least in part in an atmosphere comprising argon.Organometallic forms of catalysts can be deposited, for example, by softor reactive landing of mass-selected ions. Soft landing of mass-selectedions is used to transfer catalytically-active metal complexes completewith organic ligands from the gas phase onto an inert surface. Thismethod can be used to prepare materials with defined active sites andthus achieve molecular design of surfaces in a highly controlled wayunder either ambient or traditional vacuum conditions. For additionaldetails see, for example, Johnson et al., Anal. Chem., 2010, 82, pp.5718-5727, and Johnson et al., Chemistry: A European Journal, 2010, 16,pp. 14433-14438, the disclosures of which are incorporated herein byreference.

In some embodiments, the weight ratio of platinum to gold is in a rangefrom 3:1 to 250:1 (in some embodiments, in a range from 5:1 to 15:1,from 3:1 to 30:1, from 30:1 to 250:1, or even 15:1 to 250:1).

In some embodiments, methods for making catalyst described hereincomprise depositing platinum and nickel from a target comprisingplatinum and nickel (e.g., a Pt₃Ni₇ target) and depositing gold from atarget comprising gold. In some embodiments, layers comprising platinumand nickel have a planar equivalent thickness in a range from 0.4 nm to580 nm (in some embodiments, in a range from 0.4 nm to 72 nm) and layerscomprising gold have a planar equivalent thickness in a range from 0.01nm to 32 nm (in some embodiments, in a range from 0.01 nm to 16 nm, oreven a range from 0.01 nm to 2 nm).

In some embodiments, methods for making catalyst described hereincomprise depositing platinum from a target comprising platinum,depositing nickel from a target comprising nickel, and depositing goldfrom a target comprising gold. In some embodiments, a layer comprisingplatinum, an adjacent layer comprising nickel, and an adjacent layercomprising gold collectively have a planar equivalent thickness in arange from 0.5 nm to 50 nm (in some embodiments, in a range from 0.5 nmto 30 nm). In some embodiments, layers comprising platinum have a planarequivalent thickness in a range from 0.2 nm to 30 nm (in someembodiments, in a range from 0.2 nm to 20 nm, or even 0.2 nm to 10 nm),layers comprising nickel have a planar equivalent thickness in a rangefrom 0.2 nm to 50 nm (in some embodiments, in a range from 0.2 nm to 25nm, or even 0.2 nm to 10 nm) and layers comprising gold have a planarequivalent thickness in a range from 0.01 nm to 20 nm (in someembodiments, in a range from 0.01 nm to 10 nm, 0.01 nm to 5 nm, 0.02 nmto 5 nm, 0.02 nm to 1 nm, or even 0.1 nm to 1 nm). In some embodiments,the weight ratio of platinum to gold is in a range from 3:1 to 250:1 (insome embodiments, in a range from 5:1 to 15:1, from 3:1 to 30:1, from30:1 to 250:1, or even 15:1 to 250:1).

In some embodiments, at least one layer comprising platinum and nickel(including a layer(s) comprising platinum and nickel or a layercomprising platinum, nickel, and gold) is nanoporous (e.g., pores withdiameters in a range from 1 nm to 10 nm (in some embodiments, in a rangefrom 2 nm to 8 nm, or even 3 nm to 7 nm)). In some embodiments, at least2, 3, 4, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, or even at least275 layers comprising platinum and nickel are nanoporous.

The nanoporosity can be provided by dealloying the catalyst material toremove a portion of the nickel. In general, dealloying can beaccomplished by techniques known in the art, including via“free-corrosion” approaches (e.g., immersion in acid) or viaelectrochemical processing (e.g., potential cycling in acidic media).Nanoporosity formation typically occurs in alloys comprising at leasttwo components with sufficiently different dissolution rates in thedealloying medium and when the more noble component has sufficientsurface mobility. For additional details see, for example, Erlebacher etal., Nature, 2001, 410, pp. 450-453; and U.S. Pat. No. 6,805,972 B2(Erlebacher et al.); U.S. Pat. No. 8,673,773 B2 (Opperman et al.); andU.S. Pat. No. 8,895,206 B2 (Erlebacher et al.), the disclosures of whichare incorporated herein by reference.

In some embodiments, the catalyst material is annealed. In someembodiments, the catalyst is annealed before dealloying. In general,annealing can be done by techniques known in the art, including heatingthe catalyst material via, for example, in an oven or furnace, with alaser, and with infrared techniques. Annealing can be conducted, forexample, in inert or reactive gas environments. Although not wanting tobe bound by theory, it is believed annealing can induce structuralchanges on the atomic scale, which can influence activity and durabilityof catalysts. Further, it is believed annealing nanoscale particles andfilms can induce mobility in the atomic constituent(s), which can causegrowth of particles or thin film grains. In the case of multi-elementmixtures, alloys, or layered particles and films, it is believedannealing can induce, for example, segregation of components within theparticle or film to the surface, formation of random, disordered alloys,and formation of ordered intermetallics, depending upon the componentelement properties and the annealing environment. For additional detailsregarding annealing see, for example, van der Vliet et al., NatureMaterials, 2012, 11, pp. 1051-1058; Wang et al., Nature Materials, 2013,12, pp. 81-87, and U.S. Pat. No. 8,748,330 B2 (Debe et al.), thedisclosures of which are incorporated herein by reference.

In some embodiments, methods for making catalysts described hereincomprise:

depositing platinum and nickel from a target comprising platinum andnickel to provide at least one layer comprising platinum and nickel (insome embodiments, repeatedly depositing from the target to providemultiple layers);

dealloying at least one layer comprising platinum and nickel to removenickel from at least one layer; and

depositing a layer comprising gold from a target comprising gold. Insome embodiments, there are pores with diameters in a range from 1 nm to10 nm (in some embodiments, in a range from 2 nm to 8 nm, or even 3 nmto 7 nm) where the nickel was removed. In some embodiments, the targetis a Pt₃Ni₇ target.

In some embodiments, methods for making catalysts described hereincomprise:

depositing platinum from a target comprising platinum to provide atleast one layer comprising platinum;

depositing nickel from a target comprising nickel to provide at leastone layer comprising nickel;

dealloying at least one layer comprising platinum and nickel to removenickel from at least one layer; and

depositing a layer comprising gold from a target comprising gold. Insome embodiments, depositing the layers to provide alternating layersrespectively comprising platinum or nickel. In some embodiments, thereare pores with diameters in a range from 1 nm to 10 nm (in someembodiments, in a range from 2 nm to 8 nm, or even 3 nm to 7 nm) wherethe nickel was removed.

In some embodiments, methods for making catalysts described hereincomprise:

depositing platinum and nickel from a target comprising platinum andnickel to provide a first layer comprising platinum and nickel;

depositing a layer comprising gold from a target comprising gold;

repeating the preceding two steps, in order, at least once (in someembodiments, repeating 2, 3, 4, 5, 10, 15, 20, 25, 50, 75, 100, 150,200, 250, or even at least 275 times); and

dealloying at least one layer comprising platinum and nickel to removenickel from the layer. In some embodiments, there are pores withdiameters in a range from 1 nm to 10 nm (in some embodiments, in a rangefrom 2 nm to 8 nm, or even 3 nm to 7 nm) where the nickel was removed.In some embodiments, the target is a Pt₃Ni₇ target.

Catalysts described herein are useful, for example, in fuel cellmembrane electrode assemblies (MEAs). “Membrane electrode assembly”refers to a layered sandwich of fuel cell materials comprising amembrane, anode and cathode electrode layers, and gas diffusion layers.Typically, the cathode catalyst layer comprises a catalyst describedherein, although in some embodiments, the anode catalyst layerindependently comprises a catalyst described herein.

An MEA comprises, in order:

a first gas distribution layer having first and second opposed majorsurfaces;

an anode catalyst layer having first and second opposed major surfaces,the anode catalyst comprising a first catalyst;

an electrolyte membrane;

a cathode catalyst layer having first and second opposed major surfaces,the cathode catalyst comprising a second catalyst; and

a second gas distribution layer having first and second opposed majorsurfaces.

Electrolyte membranes conduct reaction intermediate ions between theanode and cathode catalyst layers. Electrolyte membranes preferably havehigh durability in the electrochemical environment, including chemicaland electrochemical oxidative stability. Electrolyte membranespreferably have low ionic resistance for the transport of the reactionintermediate ions, but are relatively impermeable barriers for otherions, electrons, and reactant species. In some embodiments, theelectrolyte membrane is a proton exchange membrane (PEM), which conductscations. In PEM fuel cells, the electrolyte membrane preferably conductsprotons. PEMs are typically a partially fluorinated or perfluorinatedpolymer comprised of a structural backbone and pendant cation exchangegroups, PEMs, are available, for example, from E. I. du Pont de Nemoursand Company, Wilmington, Del., under the trade designation “NAFION;”Solvay, Brussels, Belgium, under the trade designation “AQUIVION;” 3MCompany, St. Paul, Minn., under the designation “3M PFSA MEMBRANE;” andAsahi Glass Co., Tokyo, Japan, under the trade designation “FLEMION.”

A gas distribution layer generally delivers gas evenly to the electrodesand, in some embodiments, conducts electricity. It also provides forremoval of water in either vapor or liquid form, in the case of a fuelcell. Gas distribution layers are typically porous to allow reactant andproduct transport between the electrodes and the flow field. Sources ofgas distribution layers include carbon fibers randomly oriented to formporous layers, as well as non-woven paper or woven fabrics. Thenon-woven carbon papers are available, for example, from MitsubishiRayon Co., Ltd., Tokyo, Japan, under the trade designation “GRAFILU-105;” Toray Corp., Tokyo, Japan, under the trade designation “TORAY;”AvCarb Material Solutions, Lowell, Mass., under the trade designation“AVCARB;” SGL Group, the Carbon Company, Wiesbaden, Germany, under thetrade designation “SIGRACET;” Freudenberg FCCT SE & Co. KG, Fuel CellComponent Technologies, Weinheim, Germany, under the trade designation“FREUDENBERG;” and Engineered Fibers Technology (EFT), Shelton, Conn.,under the trade designation “SPECTRACARB GDL.” The woven carbon fabricsor cloths are available, for example, from Electro Chem Inc., Woburn,Mass., under the trade designations “EC-CC1-060” and “EC-AC-CLOTH;”NuVant Systems Inc., Crown Point, Ind., under the trade designations“ELAT-LT” and “ELAT;” BASF Fuel Cell GmbH, North America, under thetrade designation “E-TEK ELAT LT;” and Zoltek Corp., St. Louis, Mo.,under the trade designation “ZOLTEK CARBON CLOTH.” The non-woven paperor woven fabrics can be treated to modify its' hydrophobicity (e.g.,treatment with a polytetrafluoroethylene (PTFE) suspension withsubsequent drying and annealing). Gas dispersion layers often comprise aporous layer of sub-micrometer electronically-conductive particles(e.g., carbon), and a binder (e.g., PTFE). Although not wanting to bebound by theory, it is believed that gas dispersion layers facilitatereactant and product water transport between the electrode and the gasdistribution layers.

At least one of the anode or cathode catalyst has whiskers with catalystmaterial described herein. The “other catalyst layer” can be aconventional catalyst known in the art, and provided by techniques knownin the art (e.g., U.S. Pat. No. 5,759,944 (Buchanan et al.), U.S. Pat.No. 5,068,161 (Keck et al.), and U.S. Pat. No. 4,447,506 (Luczak etal.)), the disclosures of which are incorporated herein by reference.

In some embodiments, the cathode and/or anode catalyst layer compriseswhiskers with catalyst material described herein.

A fuel cell is an electrochemical device that combines hydrogen fuel andoxygen from the air to produce electricity, heat, and water. Fuel cellsdo not utilize combustion, and as such, fuel cells produce little, ifany, hazardous effluents. Fuel cells convert hydrogen fuel and oxygendirectly into electricity, and can be operated at much higherefficiencies than can internal combustion electric generators, forexample.

Referring to FIG. 2, exemplary fuel cell 200 includes first gasdistribution layer 201 adjacent to anode 203. Adjacent anode 203 is anelectrolyte membrane 204. Cathode 205 is situated adjacent electrolytemembrane 204, and second gas distribution layer 207 is situated adjacentcathode 205. In operation, hydrogen fuel is introduced into the anodeportion of fuel cell 200, passing through first gas distribution layer201 and over anode 203. At anode 203, the hydrogen fuel is separatedinto hydrogen ions (H) and electrons (e).

Electrolyte membrane 204 permits only the hydrogen ions or protons topass through electrolyte membrane 204 to the cathode portion of fuelcell 200. The electrons cannot pass through electrolyte membrane 204and, instead, flow through an external electrical circuit in the form ofelectric current. This current can power an electric load 217, such asan electric motor, or be directed to an energy storage device, such as arechargeable battery.

Oxygen flows into the cathode side of fuel cell 200 via seconddistribution layer 207. As the oxygen passes over cathode 205, oxygen,protons, and electrons combine to produce water and heat.

Exemplary Embodiments

-   1A. A catalyst comprising nanostructured element comprising    microstructured whiskers having an outer surface at least partially    covered by a catalyst material having the formula    Pt_(x)Ni_(y)Au_(z), wherein x is in a range from 27.3 to 29.9, y is    in a range from 63.0 to 70.0, and z is in a range from 0.1 to 9.6    (in some embodiments, x is in a range from 29.4 to 29.9, y is in a    range from 68.9 to 70.0, and z is in a range from 0.1 to 2.0; or    even x is in a range from 29.7 to 29.9, y is in a range from 69.4 to    70.0, and z is in a range from 0.1 to 0.9).-   2A. The catalyst of Exemplary Embodiment 1A, wherein the catalyst    material comprises a layer comprising platinum and nickel and a    layer comprising gold on the layer comprising platinum and nickel.-   3A. The catalyst of Exemplary Embodiment 2A, wherein the layer(s)    comprising platinum and nickel collectively has a planar equivalent    thickness up to 600 nm (in some embodiments, up to 575 nm, 550 nm,    500 nm, 400 nm, 300 nm, 200 nm, 100 nm, 75 nm, 50 nm, 25 nm, 10 nm,    5 nm, 2.5 nm, 1 nm, or even up to two monolayers (e.g., 0.4 nm); in    some embodiments, in a range from 0.4 nm to 600 nm, 0.4 nm to 500    nm, 1 nm to 500 nm, 5 nm to 500 nm, 10 nm to 500 nm, 10 nm to 400    nm, or even 40 nm to 300 nm) and the layer comprising gold has a    planar equivalent thickness up to 50 nm (in some embodiments, up to    45 nm, 40 nm, 35 nm, 30 nm, 25 nm, 20 nm, 15 nm, 10 nm, 5 nm, 4 nm,    3 nm, 2 nm, 1 nm, a monolayer (e.g., 0.2 nm) or even less than a    monolayer (e.g., 0.01 nm); in some embodiments, in a range from 0.01    nm to 50 nm, 1 nm to 50 nm, 5 nm to 40 nm, or even 5 nm to 35 nm).-   4A. The catalyst of Exemplary Embodiment 3A, wherein each layer    independently has a planar equivalent thickness up to 100 nm (in    some embodiments, up to 50 nm, 20 nm, 15 nm, 10 nm, 5 nm, 4 nm, 3    nm, 2 nm, 1 nm, a monolayer (e.g., 0.2 nm), or even up to less than    a monolayer (e.g. 0.01 nm); in some embodiments, in a range from    0.01 nm to 100 nm, 0.01 nm to 50 nm, 0.1 nm to 15 nm, 0.1 nm to 10    nm, or even 1 nm to 5 nm).-   5A. The catalyst of Exemplary Embodiment 1A, wherein the catalyst    material comprises alternating layers comprising platinum and nickel    and layers comprising gold (i.e., a layer comprising platinum and    nickel, a layer comprising gold, a layer comprising platinum and    nickel, a layer comprising gold, etc.). In some embodiments, at    least 2, 3, 4, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, or    even at least 275 sets of the alternating layers.-   6A. The catalyst of Exemplary Embodiment 5A, wherein each layer    independently has a planar equivalent thickness up to 100 nm (in    some embodiments, up to 50 nm, 20 nm, 15 nm, 10 nm, 5 nm, 4 nm, 3    nm, 2 nm, 1 nm, a monolayer (e.g., 0.2 nm), or even up to less than    a monolayer (e.g. 0.01 nm); in some embodiments, in a range from    0.01 nm to 100 nm, 0.01 nm to 50 nm, 0.1 nm to 15 nm, 0.1 nm to 10    nm, or even 1 nm to 5 nm).-   7A. The catalyst of Exemplary Embodiment 1A, wherein the catalyst    material comprises a layer comprising platinum, a layer comprising    nickel on the layer comprising platinum, and a layer comprising gold    on the layer comprising nickel.-   8A. The catalyst of Exemplary Embodiment 1A, wherein the catalyst    material comprises a layer comprising nickel, a layer comprising    platinum on the layer comprising nickel, and a layer comprising gold    on the layer comprising platinum.-   9A. The catalyst of any preceding A Exemplary Embodiment, wherein at    least one layer comprising both platinum and nickel is nanoporous.    In some embodiments, at least 2, 3, 4, 5, 10, 15, 20, 25, 50, 75,    100, 150, 200, 250, or even at least 275 layers comprising platinum    and nickel are nanoporous (e.g., pores with diameters in a range    from 1 nm to 10 nm (in some embodiments, in a range from 2 nm to 8    nm, or even 3 nm to 7 nm)).-   10A. The catalyst of any preceding A Exemplary Embodiment having an    exposed gold surface layer.-   11A. The catalyst of Exemplary Embodiment 1A, wherein the catalyst    material comprises repeating sequential individual layers of    platinum, nickel, and gold. In some embodiments, at least 2, 3, 4,    5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, or even at least 275    sets of the repeating layers.-   12A. The catalyst of Exemplary Embodiment 11A, wherein at least one    layer comprising platinum, nickel, and gold is nanoporous. In some    embodiments, at least 2, 3, 4, 5, 10, 15, 20, 25, 50, 75, 100, 150,    200, 250, or even at least 275 layers comprising platinum, nickel,    and gold are nanoporous (e.g., pores with diameters in a range from    1 nm to 10 nm (in some embodiments, in a range from 2 nm to 8 nm, or    even 3 nm to 7 nm)).-   13A. The catalyst of any preceding A Exemplary Embodiment, wherein    the weight ratio of platinum to gold is in a range from 3:1 to 250:1    (in some embodiments, in a range from 5:1 to 15:1, from 3:1 to 30:1,    from 30:1 to 250:1, or even 15:1 to 250:1).-   14A. A fuel cell membrane electrode assembly comprising the catalyst    of any preceding A Exemplary Embodiment.-   1B. A method of dealloying a catalyst, the method comprising    dealloying at least some layers comprising platinum and nickel to    remove nickel from at least one layer to provide catalyst of    Exemplary Embodiments 1A to 13A. In some embodiments, there are    pores with diameters in a range from 1 nm to 10 nm (in some    embodiments, in a range from 2 nm to 8 nm, or even 3 nm to 7 nm)    where the nickel was removed.-   1C. A method comprising annealing the catalyst of Exemplary    Embodiment 1B before dealloying.-   1D. A method comprising annealing the catalyst of Exemplary    Embodiments 1A to 13A.-   1E. A method of making the catalyst of any of Exemplary Embodiments    1A to 13A, the method comprising depositing platinum and nickel from    a target comprising platinum and nickel and depositing gold from a    target comprising gold.-   2E. The method of Exemplary Embodiment 1E, wherein the target is a    Pt₃Ni₇ target.-   3E. The method of any preceding E Exemplary Embodiment, wherein    layers comprising platinum and nickel have a planar equivalent    thickness in a range from 0.4 nm to 580 nm (in some embodiments, in    a range from 0.4 nm to 72 nm) and layers comprising gold have a    planar equivalent thickness in a range from 0.01 nm to 32 nm (in    some embodiments, in a range from 0.01 nm to 16 nm, or even a range    from 0.01 nm to 2 nm).-   4E. The method of any preceding E Exemplary Embodiment, further    comprising dealloying at least some layers comprising platinum and    nickel to remove nickel from at least one layer. In some    embodiments, there are pores with diameters in a range from 1 nm to    10 nm (in some embodiments, in a range from 2 nm to 8 nm, or even 3    nm to 7 nm) where the nickel was removed.-   5E. The method of any of Exemplary Embodiments 1E to 3E, further    comprising annealing the catalyst.-   6E. The method of Exemplary Embodiment 5E, further comprising    dealloying at least a portion of the annealed catalyst.-   1F. A method of making the catalyst of any of Exemplary Embodiments    1A to 13A, the method comprising depositing platinum from a target    comprising platinum, depositing nickel from a target comprising    nickel, and depositing gold from a target comprising gold.-   2F. The method of Exemplary Embodiment 1F, wherein a layer    comprising platinum, an adjacent layer comprising nickel, and an    adjacent layer comprising gold collectively having a planar    equivalent thickness in a range from 0.5 nm to 50 nm (in some    embodiments, in a range from 0.5 nm to 30 nm).-   3F. The method of Exemplary Embodiment 1F, wherein layers comprising    platinum have a planar equivalent thickness in a range from 0.2 nm    to 30 nm (in some embodiments, in a range from 0.2 nm to 20 nm, or    even 0.2 nm to 10 nm), layers comprising nickel have a planar    equivalent thickness in a range from 0.2 nm to 50 nm (in some    embodiments, in a range from 0.2 nm to 25 nm, or even 0.2 nm to 10    nm) and layers comprising gold have a planar equivalent thickness in    a range from 0.01 nm to 20 nm (in some embodiments, in a range from    0.01 nm to 10 nm, 0.01 nm to 5 nm, 0.02 nm to 5 nm, 0.02 nm to 1 nm,    or even 0.1 nm to 1 nm).-   4F. The method of any preceding F Exemplary Embodiment, wherein the    weight ratio of platinum to gold is in a range from 3:1 to 250:1 (in    some embodiments, in a range from 5:1 to 15:1, from 3:1 to 30:1,    from 30:1 to 250:1, or even 15:1 to 250:1).-   5F. The method of any preceding F Exemplary Embodiment, further    comprising annealing the catalyst.-   6F. The method of any preceding F Exemplary Embodiment, further    comprising dealloying at least some layers comprising platinum and    nickel to remove nickel from at least one layer. In some    embodiments, there are pores with diameters in a range from 1 nm to    10 nm (in some embodiments, in a range from 2 nm to 8 nm, or even 3    nm to 7 nm) where the nickel was removed.-   1G. A method of making the catalyst of any of Exemplary Embodiments    1A to 13A, the method comprising:

depositing platinum and nickel from a target comprising platinum andnickel to provide at least one layer comprising platinum and nickel (insome embodiments, repeatedly depositing from the target to providemultiple layers);

dealloying at least one layer comprising platinum and nickel to removenickel from at least one layer; and

depositing a layer comprising gold from a target comprising gold. Insome embodiments, there are pores with diameters in a range from 1 nm to10 nm (in some embodiments, in a range from 2 nm to 8 nm, or even 3 nmto 7 nm) where the nickel was removed.

-   2G. The method of Exemplary Embodiment 1G, further comprising    annealing the layers comprising platinum and nickel.-   3G. The method of any preceding G Exemplary Embodiment, wherein the    target is a Pt₃Ni₇ target.-   4G. The method of any preceding G Exemplary Embodiment, wherein    layers comprising platinum and nickel have a planar equivalent    thickness in a range from 0.4 nm to 70 nm (in some embodiments, in a    range from 0.4 nm to 1 nm, 0.4 nm to 5 nm, 1 nm to 25 nm, or even 1    nm to 10 nm) and layers comprising gold have a planar equivalent    thickness in a range from 0.01 nm to 20 nm (in some embodiments, in    a range from 0.01 nm to 10 nm, 0.01 nm to 5 nm, 0.02 nm to 2.5 nm,    or even 0.02 nm to 1 nm).

1H. A method of making the catalyst of any of Exemplary Embodiments 1Ato 13A, the method comprising:

depositing platinum from a target comprising platinum to provide atleast one layer comprising platinum;

depositing nickel from a target comprising nickel to provide at leastone layer comprising nickel;

dealloying at least one layer comprising platinum and nickel to removenickel from at least one layer; and

depositing a layer comprising gold from a target comprising gold. Insome embodiments, depositing the layers to provide alternating layersrespectively comprising platinum or nickel. In some embodiments, thereare pores with diameters in a range from 1 nm to 10 nm (in someembodiments, in a range from 2 nm to 8 nm, or even 3 nm to 7 nm) wherethe nickel was removed.

-   2H. The method of Exemplary Embodiment 1H, further comprising    annealing the layers comprising at least one of platinum and nickel    before dealloying.-   3H. The method of any preceding H Exemplary Embodiment, wherein    layers comprising platinum and nickel have a planar equivalent    thickness in a range from 0.4 nm to 70 nm (in some embodiments, in a    range from 0.4 nm to 1 nm, 0.4 nm to 5 nm, 1 nm to 25 nm, or even 1    nm to 10 nm) and layers comprising gold have a planar equivalent    thickness in a range from 0.01 nm to 20 nm (in some embodiments, in    a range from 0.01 nm to 10 nm, 0.01 nm to 5 nm, 0.02 nm to 2.5 nm,    or even 0.02 nm to 1 nm).-   1I. A method of making the catalyst of any of Exemplary Embodiments    1A to 13A, the method comprising:

depositing platinum and nickel from a target comprising platinum andnickel to provide a first layer comprising platinum and nickel;

depositing a layer comprising gold from a target comprising gold;

repeating the preceding two steps, in order, at least once (in someembodiments, repeating 2, 3, 4, 5, 10, 15, 20, 25, 50, 75, 100, 150,200, 250, or even at least 275 times); and

dealloying at least one layer comprising platinum and nickel to removenickel from the layer. In some embodiments, there are pores withdiameters in a range from 1 nm to 10 nm (in some embodiments, in a rangefrom 2 nm to 8 nm, or even 3 nm to 7 nm) where the nickel was removed.

-   2I. The method of Exemplary Embodiment 1I, wherein the target is a    Pt₃Ni₇ target.-   3I. The method of any preceding I Exemplary Embodiment, further    comprising annealing the layers before dealloying.-   4I. The method of any preceding I Exemplary Embodiment, wherein    layers comprising platinum and nickel have a planar equivalent    thickness in a range from 0.4 nm to 70 nm (in some embodiments, in a    range from 0.4 nm to 1 nm, 0.4 nm to 5 nm, 1 nm to 25 nm, or even 1    nm to 10 nm) and layers comprising gold have a planar equivalent    thickness in a range from 0.01 nm to 20 nm (in some embodiments, in    a range from 0.01 nm to 10 nm, 0.01 nm to 5 nm, 0.02 nm to 2.5 nm,    or even 0.02 nm to 1 nm).

Advantages and embodiments of this invention are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. All parts andpercentages are by weight unless otherwise indicated.

EXAMPLES Examples 1-4

Nanostructured whiskers employed as catalyst supports were madeaccording to the process described in U.S. Pat. No. 5,338,430 (Parsonageet al.), U.S. Pat. No. 4,812,352 (Debe), and U.S. Pat. No. 5,039,561(Debe), incorporated herein by reference, using as substrates themicrostructured catalyst transfer substrates (or MCTS) described in U.S.Pat. No. 6,136,412 (Spiewak et al.), also incorporated herein byreference. Perylene red pigment (i.e.,N,N′-di(3,5-xylyl)perylene-3,4:9,10-bis(dicarboximide)) (C.I. PigmentRed 149, also known as “PR149”, obtained from Clariant, Charlotte, N.C.)was sublimation vacuum coated onto MCTS with a nominal thickness of 200nm, after which it was annealed. After deposition and annealing, highlyoriented crystal structures were formed with large aspect ratios,controllable lengths of about 0.5 to 2 micrometers, widths of about0.03-0.05 micrometer and areal number density of about 30 whiskers persquare micrometer, and oriented substantially normal to the underlyingsubstrate.

Nanostructured thin film (NSTF) catalyst layers were prepared by sputtercoating catalyst films sequentially using a DC-magnetron sputteringprocess onto the layer of nanostructured whiskers. A vacuum sputterdeposition system (obtained as Model Custom Research from Mill LaneEngineering Co., Lowell, Mass.) equipped with 4 cryo-pumps (obtainedfrom Austin Scientific, Oxford Instruments, Austin, Tex.), a turbopumpand using typical Ar sputter gas pressures of about 5 mTorr (0.66 Pa),and 2 inch×10 inch (5 cm×25.4 cm) rectangular sputter targets (obtainedfrom Sophisticated Alloys, Inc., Butler, Pa.) was used. The coatingswere deposited by using ultra high purity Ar as the sputtering gas. Ptand Ni were first simultaneously deposited from a single alloy Pt₃Ni₇target (30 at. % Pt and 70 at. % Ni, obtained from Sophisticated Alloys,Butler, Pa.). 50 layers of Pt₃Ni₇ were deposited, each with about 2.8 nmplanar equivalent thickness, resulting in an areal Pt loading of about0.10 mg_(Pt)/cm². Pt₃Ni₇ catalysts deposited from a single alloy targetare referred to as “single target” (ST). Au (obtained from Materion,Mayfield Heights, Ohio) was then subsequently deposited onto the surfaceof four pieces of the Pt₃Ni₇-coated NSTF catalyst on substrate, eachwith a different Au areal loading calculated to yield 1, 2, 5, and 10at. % Au content in the electrocatalyst (Examples 1, 2, 3, and 4,respectively). The Au layer planar equivalent thickness for Examples 1,2, 3, and 4 was 2.1 nm, 4.1 nm, 9.8 nm, and 20.2 nm, respectively.Pt-to-Au weight ratios for Examples 1, 2, 3, and 4 were 29.4:1, 14.7:1,5.8:1, and 2.8:1, respectively.

Representative areas of the electrocatalysts were analyzed for bulkcomposition using X-Ray Fluorescence spectroscopy (XRF). Representativecatalyst samples were evaluated on MCTS using a wavelength dispersiveX-ray fluorescence spectrometer (obtained under the trade designation“PRIMUS II” from Rigaku Corporation, Tokyo, Japan) equipped with arhodium (Rh) X-ray source, a vacuum atmosphere, and a 20 mm diametermeasurement area. Each sample was analyzed three times to obtain theaverage and standard deviation for the measured Pt, Ni, and Au signalintensities, which are proportional to loading. The electrocatalysts'Pt, Ni, and Au areal loadings of Examples 1-4 were determined bycomparing their measured XRF intensities to the XRF intensities obtainedwith standard NSTF electrocatalysts containing Pt, Ni, and Au with knownareal loadings. From the XRF-determined Pt, Ni, and Au areal loadings,the catalysts' composition and Pt-to-Au weight ratios were calculated.The total platinum group metal (PGM) content was determined by addingthe Pt and Au areal loadings. Loading and composition information isprovided in Table 1, below.

TABLE 1 PtNi Au Loading (mg/cm²) Composition (at. %) Pt:Au WeightExample Deposition Incorporation Pt Ni Au PGM Pt Ni Au Ratio Comp. Ex. AST None 0.104 0.073 0.000 0.104 30.0 70.0 0.0 Infinite Ex. 1 ST Toplayer 0.111 0.077 0.004 0.114 29.8 69.2 1.0 29.4 Ex. 2 ST Top layer0.110 0.077 0.008 0.118 29.4 68.6 2.0 14.7 Ex. 3 ST Top layer 0.1110.078 0.019 0.130 28.5 66.6 4.9 5.8 Ex. 4 ST Top layer 0.111 0.077 0.0390.150 27.3 63.0 9.6 2.8 Ex. 5 ST Bilayer 0.113 0.078 0.021 0.134 28.766.0 5.4 5.3

The Pt_(x)Ni_(y)Au_(z) catalysts and NSTF PtCoMn coated anode catalystwhiskers (0.05 mg_(Pt)/cm², Pt₆₉Co₂₈Mn₃) on MCTS were then transferredto either side of a 24-micrometer thick proton exchange membrane(available under the trade designation “3M PFSA 825EW” (neat) from 3MCompany, St. Paul, Minn.), using a laminator (obtained under the tradedesignation “HL-101” from Chem Instruments, Inc., West Chester Township,Ohio) to form a catalyst coated membrane (CCM). The three-layer stack-upwas hand fed into the laminator with hot nip rolls at 270° F. (132° C.),150 psi (1.03 MPa) nip, and rotating at the equivalent of 0.5 fpm (0.25cm/s). Immediately after lamination, the MCTS layers were peeled back,leaving the catalyst coated whiskers embedded into either side of thePEM. The CCM was installed with identical gas diffusion layers(available under the trade designation “3M 2979 GAS DIFFUSION LAYERS”from 3M Company) on the anode and cathode in 50 cm² active area testcells (obtained under the trade designation “50 CM2 CELL HARDWARE” fromFuel Cell Technologies, Inc., Albuquerque, N. Mex.) with quad-serpentineflow fields with gaskets selected to give 10% compression of the gasdiffusion layers. The catalyst of the present invention was evaluated asthe fuel cell cathode.

After assembly, the test cells were connected to a test station(obtained under the trade designation “SINGLE FUEL CELL TEST STATION”from Fuel Cell Technologies, Inc.). The MEA was then operated for about40 hours under a conditioning protocol to achieve apparent steady stateperformance. The protocol consisted of repeated cycles of operationaland shutdown phases, each about 40 and 45 minutes in duration,respectively. In the operational phase, the MEA was operated at 75° C.cell temperature, 70° C. dew point, 101/101 kPaA H₂/Air, with constantflow rates of 800 and 1800 sccm of H₂ and air, respectively. During the40-minute operational phase, the cell voltage was alternated between5-minute long polarization cycles between 0.85 V and 0.25 V and 5-minutelong potential holds at 0.40 V. During the 45-minute shutdown phase, thecell potential was set to open circuit voltage, H₂ and air flows to thecell were halted, and the cell temperature was cooled towards roomtemperature, while liquid water was injected into the anode and cathodecell inlets at 0.26 g/min. and 0.40 g/min., respectively. Without beingbound by theory, it is believed the fuel cell conditioning protocol,which includes numerous potential cycles, may induce formation ofnanopores within the electrocatalyst.

After conditioning the MEAs, the electrocatalysts were characterized forrelevant beginning of life (BOL) characteristics, including catalystactivity, surface area, and operational performance under relevantH₂/Air test conditions, described as follows.

The cathode oxygen reduction reaction (ORR) absolute activity wasmeasured with saturated 150 kPaA H₂/O₂, 80° C. cell temperature for 1200seconds at 900 mV vs. the 100% H₂ reference/counter electrode. The ORRabsolute activity (A/cm² or mA/cm²) was obtained by adding the measuredcurrent density after 1050 seconds of hold time and the electronicshorting and hydrogen crossover current densities, estimated from 2 mV/scyclic voltammograms measured with N₂ fed to the working electrodeinstead of O₂. The electrocatalyst mass activity, a measure of thecatalyst activity per unit precious metal content, is calculated bydividing the corrected ORR absolute activity (A/cm² _(planar)) by thecathode Pt or PGM areal loading (mg/cm²) to obtain the mass activity(A/mg_(Pt) or A/mg_(PGM)). The electrocatalyst mass activity is providedin Table 2, below, and FIGS. 3A and 3B.

TABLE 2 Au ORR Mass H₂/Air Au Content Specific Area Activity PerformanceExample Incorporation at. % m₂/g_(Pt) m₂/g_(PGM) A/mg_(Pt) A/mg_(PGM)Volts Comp. Ex. A None 0 16.1 16.1 0.35 0.35 0.892 Ex. 1 Top layer 1.014.9 14.4 0.22 0.21 0.884 Ex. 2 Top layer 2.0 11.5 10.8 0.17 0.16 0.881Ex. 3 Top layer 4.9 6.0 5.1 0.07 0.06 0.835 Ex. 4 Top layer 9.6 1.5 1.10.04 0.03 0.746 Ex. 5 Bilayer 5.4 9.8 8.2 0.15 0.12 0.878

The cathode catalyst surface enhancement factor (SEF, m² _(Pt)/m²_(planar) or analogously cm² _(Pt)/cm² _(planar)) was measured viacyclic voltammetry (100 mV/s, 0.65 V-0.85 V, average of 100 scans) undersaturated 101 kilopascals absolute pressure (kPaA) H₂/N₂ and 70° C. celltemperature. The SEF was estimated by taking the average of theintegrated hydrogen underpotential deposition (H_(UPD)) charge (μC/cm²_(planar)) for the oxidative and reductive waves and dividing by 220μC/cm² _(Pt). The electrocatalyst's specific surface area (m²_(Pt)/g_(pt) or m² _(Pt)/g_(PGM)), a measure of catalyst dispersion, wascalculated by dividing the SEF (m² _(Pt)/m² _(planar)) by the areal Ptor total platinum group metal (PGM) loading (g_(Pt)/m² _(planar or)g_(PGM)/m² _(planar)). The electrocatalyst's specific area is providedin Table 2, above, and FIGS. 3C and 3D.

The operational performance of electrocatalysts was evaluated via H₂/Airpolarization curves, measured at 80° C. cell temperature, 68° C. dewpoint, 150/150 kPaA H₂/Air, with constant stoichiometry of 2.0 H₂ and2.5 for air. The current density was initially set to 20 mA/cm², andthen stepwise increased while the cell voltage was maintained above 0.40V, after which the current density was stepwise decreased back to 20mA/cm². The cell was held at each current density for 2 minutes. Thecell voltage at a specific current density, 20 mA/cm², is reported as“H₂/Air Performance” and is reported in Table 2, above, and FIG. 3E.

Example 2 catalyst was additionally evaluated under an acceleratedstress test (AST), which evaluated the stability of the electrocatalystmetal. In this test, the cell was operated at 80° C. cell temperature,200/200 sccm H₂/N₂, 101 kPaA, 100% inlet relative humidity (RH), and thecathode electrode potential was cycled between 0.6 V-1.0 V vs. thehydrogen counter/reference electrode at a scan rate of 50 mV/s. Withoutbeing bound by theory, it is believed the AST protocol, which includesnumerous potential cycles, may induce formation of nanopores within theelectrocatalyst. After 10 or 15 thousand AST cycles, the MEA wasreconditioned for about 16 hours using the initial conditioningprotocol, after which the cathode surface area, ORR activity, and H₂/Airpolarization curves were again measured to determine the rate and extentof performance loss. This process of AST, reconditioning, andcharacterization was repeated such that the cell was exposed to a totalof 30,000 AST cycles. The changes in specific area, mass activity, andH₂/Air performance after the 30,000 AST cycles are listed in Table 3,below.

TABLE 3 Au ORR Mass H₂/Air Au Content Specific Area Activity PerformanceExperiment Incorporation at. % m₂/g_(PGM) % Change A/mg_(PGM) % ChangeVolts Change Comp. Ex. A None 0 16.1 −39.5 0.35 −61.6 0.892 −0.037 Ex. 2Top layer 2.0 10.8 −12.4 0.16 −37.5 0.881 −0.025 Ex. 5 Bilayer 5.4 8.2−34.4 0.12 −42.5 0.878 −0.032

Example 5

Example 5 was prepared and evaluated as described for Examples 1-4,except that the Au metal was incorporated into the alloy duringdeposition of the Pt₃Ni₇.

A first “ST” Pt₃Ni₇ layer was deposited with about 1 nm planarequivalent thickness, onto which an Au layer was deposited. The Auplanar equivalent thicknesses was about 0.08 nm. This deposition processwas repeated 135 times until an areal Pt loading of about 0.10mg_(Pt)/cm² was achieved.

Loading and composition information is provided in Table 1, above. Thecatalyst mass activity, specific area, and H₂/Air performance afterinitial conditioning are reported in Table 2, above, and shown in FIGS.3A, 3B, 3C, 3D, and 3E. The changes in specific area, mass activity, andH₂/Air performance after the 30,000 AST cycles tested are listed inTable 3, above.

Comparative Example A

Comparative Example A was prepared and evaluated as described forExample 1, except that no Au was incorporated into the catalyst.

Loading and composition information is provided in Table 1, above. Thecatalyst specific area, mass activity, and H₂/Air performance afterinitial conditioning are reported in Table 2, above, and shown in FIGS.3A, 3B, 3C, 3D, and 3E. The changes in specific area, mass activity, andH₂/Air performance after the 30,000 AST cycles tested are listed inTable 3, above.

Comparative Example B

Comparative Example B was prepared and evaluated as described forComparative Example A, except that during electrocatalyst deposition thePt₃Ni₇ loading and layer planar equivalent thickness differed and it wasnot evaluated under the AST durability test. Three layers of Pt₃Ni₇ weredeposited, each with about 52 nm planar equivalent thickness, resultingin a Pt areal loading of about 0.125 mg_(Pt)/cm².

Loading and composition information is provided in Table 4, below.

TABLE 4 PtNi Au Loading (mg/cm²) Composition (at. %) Pt:Au WeightExample Deposition Incorporation Pt Ni Au PGM Pt Ni Au Ratio Comp. Ex. BST None 0.125 0.088 0.000 0.125 29.9 70.1 0.0 Infinite Ex. 6 ST Toplayer 0.125 0.088 0.0005 0.126 29.9 70.0 0.1 250 Ex. 7 ST Top layer0.125 0.088 0.0010 0.126 29.9 69.9 0.2 125 Ex. 8 ST Top layer 0.1250.088 0.0014 0.126 29.8 69.8 0.3 86.8 Ex. 9 ST Top layer 0.125 0.0880.0019 0.127 29.8 69.7 0.5 64.4 Ex. 10 ST Top layer 0.125 0.088 0.00390.129 29.7 69.4 0.9 32.4

The catalyst specific area, mass activity, and H₂/Air performance afterinitial conditioning are reported in Table 5, below.

TABLE 5 Au ORR Mass H₂/Air Au Content Specific Area Activity PerformanceExample Incorporation at. % m₂/g_(Pt) m/g_(PGM) A/mg_(Pt) A/mg_(PGM)Volts Comp. Ex. B None 0.0 13.4 13.4 0.39 0.39 0.903 Ex. 6 Top layer 0.114.2 14.1 0.32 0.32 0.901 Ex. 7 Top layer 0.2 13.8 13.6 0.35 0.35 0.894Ex. 8 Top layer 0.3 13.9 13.7 0.34 0.33 0.901 Ex. 9 Top layer 0.5 13.713.3 0.36 0.35 0.893 Ex. 10 Bilayer 0.9 13.4 13.4 0.39 0.39 0.903

Examples 6-10

Examples 6-10 were prepared and evaluated as described for ComparativeExample B, except that Au was deposited onto the surface afterdeposition of Pt₃Ni₇, Au was deposited with an e-beam coater, and Auloading was determined within the e-beam coater.

For Example 6, a layer of Au was coated onto NSTF catalyst preparedabove by using an e-beam coater equipment (obtained as Model MK-50, fromCHA Industries, Fremont, Calif.). One planetary rotator mounted withNSTF catalyst as a substrate rotated inside the system under vacuum withthe 270 degree electron beam heating the Au source to its sublimationpoint. As the Au sublimated, the deposited amount of Au and thedeposition rate were monitored in real time using a quartz crystalmonitor (obtained under the trade designation “INFICON;” Model 6000,from CHA Industries, Fremont, Calif.). Once the Au deposit loading of0.5 microgram/cm² on the NSTF catalyst was attained, the power to theelectron beam was terminated and the deposition ended. The system wasthen vented and the substrates removed. Examples 7, 8, 9, and 10 wereprepared as described for Example 6, but the Au loadings were 1.0, 1.4,1.9, and 3.9 microgram/cm², respectively.

Au content for Examples 6, 7, 8, 9, and 10 were 0.1, 0.2, 0.3, 0.5, and0.9 at. %, respectively. Au layer planar equivalent thicknesses forExamples 6, 7, 8, 9, and 10 were 0.26 nm, 0.52 nm, 0.75 nm, 1.0 nm, and2.0 nm, respectively. Pt-to-Au weight ratios for Examples 6, 7, 8, 9,and 10 were 250:1, 125:1, 86.8:1, 64.4:1, and 32.4:1, respectively.

Loading and composition information is provided in Table 4, above. Thecatalyst specific area, mass activity, and H₂/Air performance afterinitial conditioning are reported in Table 5, above.

Foreseeable modifications and alterations of this disclosure will beapparent to those skilled in the art without departing from the scopeand spirit of this invention. This invention should not be restricted tothe embodiments that are set forth in this application for illustrativepurposes.

1. A catalyst comprising nanostructured element comprisingmicrostructured whiskers having an outer surface at least partiallycovered by a catalyst material having the formula Pt_(x)Ni_(y)Au_(z),wherein x is in a range from 27.3 to 29.9, y is in a range from 63.0 to70.0, and z is in a range from 0.1 to 9.6.
 2. The catalyst of claim 1,wherein x is in a range from 29.4 to 29.9, y is in a range from 68.6 to70.0, and z is in a range from 0.1 to 2.0.
 3. The catalyst of claim 1,wherein the catalyst material comprises a layer comprising platinum andnickel and a layer comprising gold on the layer comprising platinum andnickel.
 4. The catalyst of claim 3, wherein each layer independently hasa planar equivalent thickness up to 25 nm.
 5. The catalyst of claim 1,wherein the catalyst material comprises alternating layers comprisingplatinum and nickel and layers comprising gold.
 6. The catalyst of claim5, wherein each layer independently has a planar equivalent thickness upto 25 nm.
 7. The catalyst of claim 1, wherein the catalyst materialcomprises a layer comprising platinum, a layer comprising nickel on thelayer comprising platinum, and a layer comprising gold on the layercomprising nickel.
 8. The catalyst of claim 1, wherein the catalystmaterial comprises a layer comprising nickel, a layer comprisingplatinum on the layer comprising nickel, and a layer comprising gold onthe layer comprising platinum.
 9. The catalyst of claim 1 having anexposed gold surface layer.
 10. The catalyst of claim 1, wherein theweight ratio of platinum to gold is in a range from 3:1 to 250:1.
 11. Afuel cell membrane electrode assembly comprising the catalyst ofclaim
 1. 12. A method comprising annealing the catalyst of claim
 1. 13.A method of making the catalyst of claim 1, the method comprisingdepositing platinum and nickel from a target comprising platinum andnickel and depositing gold from a target comprising gold.
 14. A methodof making the catalyst of claim 1, the method comprising depositingplatinum from a target comprising platinum, depositing nickel from atarget comprising nickel, and depositing gold from a target comprisinggold.